1. Field of the Invention
The present invention relates generally to a magnetic random access memory (MRAM), and more particularly, to a MRAM cell using a single crystal self-aligned diode and methods for operating and fabricating the same.
2. Description of the Related Art
The magnetic random access memory (MRAM) is a memory cell that is capable of performing nonvolatile memory operations. A MRAM cell consists of two devices: a MRAM device and a selective device. The MRAM device of a MRAM cell is used to store information, whereas the selective device of a MRAM cell is used for preventing the MRAM device from being affected by other MRAM cells in a MRAM array, such as the leakage current. A MRAM cell has high speed, low power consumption, and high integration density.
Formed by multi-layer ferromagnetic thin films, the MRAM device of a MRAM cell can have either in-plane or perpendicular magnetization directions relative to the surfaces of the ferromagnetic thin films. Because the resistance of the MRAM device changes according to the magnetization directions formed in the multi-layer ferromagnetic thin films, the information stored at the MRAM device of a MRAM cell is read by sensing current variations due to the resistance change.
The selective device of a MRAM cell can be either a diode or a transistor. A single crystal diode or a poly-crystal diode may be used for the selective device for a MRAM cell. However, a single crystal diode has the difficulty to shrink its size and a poly-crystal diode has a current leakage problem at the reverse bias region. Alternatively, a transistor can be used for the selective device of a MRAM cell, however, the fabrication process for a transistor is more complicated than the one for a diode. Furthermore, the size of a transistor is also larger than the size of a diode.
In view of the foregoing, there is a need for a MRAM cell using a new selective device that has small size and simple fabrication process.